[CWatters]

Been asked to build a new shelter for our chickens as they are sheltering somewhere that won't be available much longer. Normally I'd use something like shiplap or T&G boards to clad the thing but I know about red mites so was looking for ideas for suitable alternatives. 

It's possible I'll have some 1" thick oak boards left over from another project. If I leave small gaps say 3mm wide between the boards is that sufficiently wide to stop mites setting up home?

[ANHBUC]

They would probably take up residence between the frame battons and the oak boards.     There are preventative measures and treatments for redmite if you are wanting to use wood. 

If not you could make a shelter with plastic.  You could adapt a compost bin/water butt or use corrugated roofing sheets with a frame of angle iron/aluminium.  It really depends how big you need the shelter and for how many hens.

You do mean shelter and not coop don't you? 

[CWatters]

Yes shelter not coop. The site is somewhat exposed and in recent bad weather the chickens have been sheltering in the run attached to a small coop which we will need for some chicks soon.

My wife has since pointed out that mites come out at night when the chickens are in the coop not the shelter so she reckons shiplap/T&G will be ok. 

To give you a rough idea of the size I'm planning to use a single sheet of onduline for the roof, (cut in half and arranged so the corregations run the right way).

[ANHBUC]

You would think they would manufacture them with the corrugation in a choice of both directions either length or width ways.  It would make it so much easier for making coops, hutches and runs.

You could make a frame with roof and debris netting on the sides as a windbreak.